Atherosclerosis continues to be the single leading cause of mortality in Western cultures. The development of atherosclerotic lesions is thought to follow the phenotypic modulation of medial smooth muscle cells (SMC) from the contractile to the synthetic state. A variety of signals have been identified that appear to participate in this modulation including oxidative stress, cytokines and interleukins of macrophage origin and endothelial factors (endothelins and NO.). The primacy of serum hypercholesterolemia as a risk factor suggests that the molecule cholesterol may also play a role in atherogenesis. Work performed by our lab has shown that enrichment of the SMC plasma membrane with cholesterol induces alterations in SMC very similar to those seen in atherosclerosis. Moreover, these alterations are reversed by estrogen. We hypothesize that enrichment of the SMC plasma membrane with cholesterol is an important factor contributing to SMC modulation during atherogenesis, and that estrogen's ability to reverse this effect contributes to its atheroprotective actions. We will test this hypothesis in 2 aims. Aim l will determine whether cholesterol's ability to alter the SMC membrane bilayer structure, as a single, isolated and independent variable contributes to the phenotypic and gene expression alterations in SMC during atherogenesis. Aim 2 will determine whether the atheroprotective effects of estrogen are mediated A), directly at the level of the arterial SMC and B), whether the mechanism of estrogen's actions are mediated, in part, by countering cholesterol's effects on the arterial SMC membrane. For these studies,we will employ two preparations of vascular cells: 1. early passage (equal to or <3) rabbit aortic SMC, and 2, early passage (equal to or <3) human aortic and coronary artery SMC. Phenotypic alterations will be followed including cell proliferation and collagen synthesis. NFkappaB activation and the generation of reactive oxygen intermediates will be measured as potential signaling intermediates using appropriate techniques. Alterations in gene expression will be assessed by measuring message and protein levels for 2 genes we have identified to be upregulated in SMC during atherogenesis (hn-RNP-K and prolyl-4-hydroxylase) as well as genes identified by others reflecting the synthetic phenotype in SMC, collagens I and III. Combining these approaches will provide essential insights into the cellular basis for the early defects in human SMC during atherogenesis and how estrogen provides cellular protection in this disease